The present invention generally relates to an ultrasonic flaw detecting apparatus, and particularly relates to a fan-shaped scanning flaw detecting apparatus in which scanning operation with a probe is smoothly achieved even upon a curved-surface of an object to be examined, while a superior ultrasonic transmission efficiency is maintained, and in which a focused ultrasonic beam is formed so that a superior azimuth resolution can be obtained.
In a conventional ultrasonic imaging apparatus for use for medical diagnosis or flaw detection by electronically performing fan-shaped scanning with a ultrasonic beam, as discussed in "Ultrasonics" (July, 1968, pp. 153 to 159), there has been employed a system in which the phase of the transmitting and receiving operation of transducer elements constituting a linear array transducer for transmitting and receiving ultrasonic waves is controlled to cause an ultrasonic beam to perform fan-shaped scanning within a required angular range so that an ultrasonic echo image inside a section of the fan-shape is displayed.
Alternatively, as disclosed in Hitachi-Hyoron, Vol. 64, No. 3, pp. 45-50, March 1982, there has been employed another system in which fan-shaped scanning with an ultrasonic beam is performed by sequentially shifting the transmitting and receiving operation of a series of transducer elements arranged on a circular arc in a linear array transducer for transmitting and receiving ultrasonic waves.
In the list of the these two systems in which the phase or delay time of the transmitting and receiving operation of the linear array transducer is controlled to deflect an ultrasonic beam to cause the ultrasonic beam to perform fan-shaped scanning, there have been disadvantages in the following points.
(1) There is a problem that an ultrasonic wave cannot be effectively transferred if an object to be examined has a curved or rough surface because it is necessary to cause at least the ultrasonic wave emitting-and-receiving surface of the linear array transducer to acoustically contact with the object to be examined.
(2) In order to improve the azimuth resolution, a system is employed in which the relative phase relationship between the respective transducer elements is adjusted to focus the ultrasonic beam at a predetermined position on an object to be examined. There is a problem that the effective portion is only within a limited focal range and there is low azimuth resolution in portions outside the focal range.
(3) Since it is necessary to accurately control the delay operation of the respective transducer elements in order to deflect the ultrasonic beam, it is necessary to provide a complicated and expensive function for adjusting a delay network.
In the second system in which an ultrasonic beam is deflected by the shifting operation of a circular-arc transducer array, there is a problem that it is necessary to adjust the phases of the respective operative elements in order to increase its azimuth resolution. The range of beam focusing is extremely limited in the same manner as the above item (2), and there is a further problem that it is necessary to provide a function for adjusting a delay network in the same manner as the above item (3).